The present invention relates to an image display apparatus such as a monitor or a data projector having a matrix display device (hereinafter referred to as a display panel) such as a liquid crystal display panel, a digital micromirror device (DMD), a field emission display (FED), a plasma display panel (PDP), or an LED panel. More specifically, the present invention relates to an image display apparatus that displays a scaled-up image if an image size of an input image signal is smaller than a size of an effective display area of the display panel.
FIG. 7 is a diagram showing configuration of a prior art image display apparatus, which is disclosed in Japanese Patent Kokai Publication No. 10-334227 published on Dec. 18, 1998. In the image display apparatus 100 shown in FIG. 7, an image signal is supplied from a terminal 101, and a dot clock SCLK for the image signal is supplied from a terminal 102. The image signal supplied from the terminal 101 is input to a control unit 103 and a time-base converter 104. The dot clock SCLK supplied from the terminal 102 is input to the time-base converter 104. The control unit 103 outputs an output clock DCLK so that a scaled-up image is generated at a frame rate matching a rate at which the input image signal is received. The clock DCLK output by the control unit 103 is supplied to the time-base converter 104, an interpolation circuit 105, and a panel controller 106. Then, the control unit 103 outputs a buffer control signal BANK for controlling a line buffer in the time-base converter 104. The buffer control signal BANK output by the control unit 103 is supplied to the time-base converter 104. Moreover, the control unit 103 outputs a modifier signal Q for determining pixel data used for interpolation and a phase value signal PHASE for determining an interpolation coefficient. The modifier signal Q output from the control unit 103 is input to the time-base converter 104 and the interpolation circuit 105, and the phase value signal PHASE is supplied to the interpolation circuit 105.
The time-base converter 104 receives the pixel data for the input image in synchronization with the dot clock SCLK, and outputs the received pixel data in synchronization with the output clock DCLK on a different time base according to the buffer control signal BANK supplied from the control unit 103. The pixel data output from the time-base converter 104 is image data scaled up by copying (or repeating) the pixel data. The scaled-up pixel data output from the time-base converter 104 is supplied to the interpolation circuit 105. The interpolation circuit 105 performs predetermined interpolation of the pixel data of the scaled-up image, according to the modifier signal Q and the phase value signal PHASE, and outputs the results of interpolation. The pixel data of the scaled-up image subjected to interpolation and output by the interpolation circuit 105 is supplied to the panel controller 106. The panel controller 106 outputs the scaled-up image subjected to interpolation to the display panel 107 in a signal format compatible with the input interface of the display panel 107. The display panel 107 therefore displays the scaled-up image subjected to interpolation according to the output of the panel controller 106.
FIG. 8 is a block diagram showing configuration of a prior art image display apparatus, which is disclosed in Japanese Patent Kokai Publication No. 08-129356 published on May 21, 1996. In the image display apparatus 200 shown in FIG. 8, an image signal is input from a terminal 201. The input image signal is supplied to a first arithmetic circuit 202 and a control unit 203. The control unit 203 detects resolution of the image data from a synchronizing signal of the image signal and outputs a scaling factor CZ calculated from a ratio of the detected result to the resolution of the display panel 206. The control unit 203 also outputs a horizontal interpolation control signal CH and a vertical interpolation control signal CV, according to a calculated scaling factor CZ. Moreover, the control unit 203 outputs a memory control signal CM for controlling a write timing and a read timing of the frame memory 204. The control unit 203 further outputs the display control signal CP for the display panel 206. The scaling factor CZ output by the control unit 203 is supplied to the first arithmetic circuit 202 and the second arithmetic circuit 205. The horizontal interpolation control signal CH output by the control unit 203 is supplied to the first arithmetic circuit 202, and the vertical interpolation control signal CV is supplied to the second arithmetic circuit 205. The memory control signal CM output by the control unit 203 is supplied to the frame memory 204. The display control signal CP output by the control unit 203 is supplied to the display panel 206.
The first arithmetic circuit 202 performs interpolation of the input image data in consecutive dot units, according to the scaling factor CZ and the horizontal interpolation control signal CH, and outputs the image data scaled up in the horizontal direction. The horizontally scaled-up image data output by the first arithmetic circuit 202 is supplied to the frame memory 204. The frame memory 204 stores the horizontally scaled-up image data of one screen according to the memory control signal CM, and the stored image data is read out. The horizontally scaled-up image data read from the frame memory 204 is input to the second arithmetic circuit 205. The second arithmetic circuit 205 performs interpolation of the image data of consecutive two lines of the horizontally scaled-up image according to the scaling factor CZ and the vertical interpolation control signal CV. If the scaled-up image data has a lower resolution than the display panel 206, a display area that has no image data on the display panel 206 is replaced with monochromatic image data. The scaled-up image data output by the second arithmetic circuit 205 is supplied to the display panel 206. The display panel 206 displays the scaled-up image data according to the display control signal CP and displays monochromatic data in areas without image data.
Owing to the configurations as described above, the above-mentioned prior art image display apparatuses have problems as described below.
FIGS. 9A and 9B are diagrams for explaining the image display method of the prior art image display apparatus 100 shown in FIG. 7. FIG. 9A shows the numbers (720 pixels wide by 400 pixels high) of horizontal and vertical pixels of the input image signal, and FIG. 9B shows the numbers (1024 pixels wide by 768 pixels high) of horizontal and vertical pixels of the displayed image. In this example, a horizontal scaling factor is 1.42 (=1024 pixels/720 pixels), and a vertical scaling factor is 1.92 (=768 pixels/400 pixels). Accordingly, as shown in FIG. 9B, vertically distorted (vertically elongated) image is displayed. If the display panel 107 and the input image have different aspect ratios, the prior art image display apparatus 100 shown in FIG. 7 cannot display a correct scaled-up image with the same aspect ratio as that of the input image.
Unlike the image display apparatus 100 shown in FIG. 7, the prior art image display apparatus 200 shown in FIG. 8 is freed from the impossibility of maintaining the aspect ratio of the input image. However, a frame memory for one screen is needed, which results in very high cost and high difficulty in integrating the signal processing circuit other than display panel into an LSI chip.
It is an object of the present invention to provide a low-cost image display apparatus that can display a scaled-up image maintaining the aspect ratio of the input image even if the display panel and the input image have different aspect ratios.
According to the present invention, the image display apparatus comprises: a synchronizing signal decimation circuit for performing decimation of input vertical synchronizing signals to output decimated vertical synchronizing signals; an image decimation circuit for performing decimation of input image data to output decimated image data; an image scale-up circuit for scaling up the decimated image data to output scaled-up image data; a display panel for displaying an image; a driving circuit for causing the display panel to sequentially display individual frames of image according to the scaled-up image data in synchronization with the decimated vertical synchronizing signals; and a controller having information of a scaling factor of the image scale-up circuit, vertical synchronizing signals to be discarded by the synchronizing signal decimation circuit, and image data to be discarded by the image decimation circuit, the controller controlling operation of the synchronizing signal decimation circuit, the image decimation circuit, the image scale-up circuit, and the driving circuit according to the information.
Further, the image display apparatus may further comprise a delay circuit for performing delay processing on the vertical synchronizing signals to output delayed vertical synchronizing signals to the driving circuit.
Furthermore, the controller may determine the scaling factor of the image scale-up circuit according to a size of the input image data for a single frame and a size of an effective display area of the display panel.
The controller may also determine vertical synchronizing signals to be discarded by the synchronizing signal decimation circuit and image data to be discarded by the image decimation circuit according to a size of the input image data for a single frame, a size of an effective display area of the display panel, and a frequency of the input vertical synchronizing signals.
Moreover, the controller may determine vertical synchronizing signals to be discarded by the synchronizing signal decimation circuit, a delay time by the delay circuit, and image data to be discarded by the image decimation circuit according to a size of the input image data for a single frame, a size of an effective display area of the display panel, a frequency of the input vertical synchronizing signals, and an image display position in the effective display area of the display panel.
In addition, in the decimation by the image decimation circuit, the image decimation circuit selects a predetermined frame among first to N-th frames of sequentially input image data, N representing a frame number which is a certain integer not smaller than 2, outputs the selected frame of image data, and discards image data other than the selected frame of image data, in the decimation by the synchronizing signal decimation circuit, the synchronizing signal decimation circuit selects a predetermined frame among first to N-th frames of sequentially input vertical synchronization signals, outputs the selected frame of vertical synchronizing signal, and discards vertical synchronizing signals other than the selected frame of vertical synchronizing signal, and a frame number of the selected frame of image data is different from a frame number of the selected frame of vertical synchronizing signal.
The image display apparatus may further comprise an image data adding circuit for displaying a certain color at an area other than the image based on the image data in the effective display area of the display panel.
Further, the image display apparatus may further comprise an image data adding circuit for displaying a message indicating that a displayed image is based on the decimated vertical synchronizing signals and the decimated image data when the image decimation circuit performs decimation of the image data.